The process by which one visually perceives involves light entering the eye in parallel rays, which are generally bent as they pass through the cornea and lens of the eye. In the normal eye, these light rays converge, or focus, on the retina at the back of the eyeball. Electrical impulses then transmit a sharp image to the brain.
Two common vision problems nearsighted (myopia) and farsighted (hyperopia) involve improper shaped eyeballs. In the nearsighted vision problem, the eyeball is usually too long or the cornea too curved, so that the light rays entering the eye come to a focal point in front of the retina. In the farsighted vision problem, the eyeball is too short or the cornea too flat and the light rays, if they could pass through the eyeball, would converge behind the retina. Eyeglasses and contact lenses change the focal point of the light entering the eye to provide corrected vision for near and farsighted vision problems.
Another approach to correct nearsightedness and farsightedness is to change the curvature of the cornea so that images fall directly on the retina. A corneal operation termed refractive keratoplasty has been used by Dr. Jose' I. Barraquer of Bogota, Columbia. In one of Dr. Barraquer's procedures known as keratomileusis (corneal carving) the front of the cornea is sliced off. The sliced off cornea is then frozen and reshaped on its interior surface by a cryolathe. After thawing, the cornea slice is stitched back on the eye. To correct nearsightedness, under Dr. Barraquer's process, the surgeon removes tissue from the center of the cornea, thereby flattening it. In farsighted patients, tissue is removed from the periphery of the cornea to accentuate the curve. A similar operation, called keratophakia (cornea lens) is used to correct only farsightedness. In this operation, after the front of the cornea is sliced off, a reshaped donor cornea is placed on the remaining cornea. The front of the original patient's cornea is then resewn, resulting in a more sharply curved corneal structure.
An additional surgical procedure in which a donor cornea is ground and sewn onto a recepient cornea has been proposed by Dr. Herbert E. Kaufman of New Orleans. In this procedure, the epithelial layer of the cornea is removed. A cut, approximately 0.1 to 0.3 millimeters in length, is made at the periphery of the cornea, and the donor contact lens or "button" is sewn on. The donor contact lens is frozen prior to being ground and therefore has no epithelium layer and virtually no living keratocytes. The keratocytes are repopulated in the collagen of the donor contact lens from the host cornea.
In contrast to the procedure of Dr. Barraquer, the procedure of Dr. Kaufman does not remove a piece of the cornea, but only the epithelial layer of the cornea is removed with the Bowman membrane left intact. Dr. Kaufman's procedure also makes it possible for the donor cornea to be ground to the needs of a particular patient in advance of surgery. It would not be necessary therefore for the piece of cornea removed from the patient's eye or a donor eye to be ground on a lathe during the operation.
The above procedures developed by Dr. Barraquer and Dr. Kaufman involve sophisticated and somewhat complex lathing equipment and mathematical analysis. It has been proposed that precut lenticules or lamellar discs could be stored based upon predetermined dioptric correction of a patient. The ophthalmic surgeon would then, based upon a calculated preoperative dioptric correction, obtain a donor cornea previously ground to the determined correction needed by his patient. Lamellar dissection and suturing of the donor cornea would then be performed to complete the surgical operation using the living contact lenses. Lenticule preservation is discussed in an article by M. H. Friedlander entitled "Keratophakia Using Preserved Lenticules", Ophthalmology, July 1980, Volume 87, No. 7.
With the development of surgical procedures for changng the shape of the cornea to correct for myopia and hyperopia and improved lenticule preservation techniques, a need for refined surgical procedures for performing refractory keratoplasty has arisen. Particularly, a need has arisen for surgical techniques and lenticule structures fitted to the patient's cornea that ensure that the lenticule is retained by the patient's cornea. A need has thus arisen for a lenticule for use in refractive keratoplasty surgical operations that can be easily handled in a standard operating room and which has improved corneal fixation.